Most of all, Goth is a state of mind; dark, sullen, talks of death and morbid things, wear black clothes and spiked dog collars, with a bit or a lot Punk style, etc.
Merriam-Webster’s Collegiate Dictionary, 11th ed. says: “Goth: ...rock music marked by dark and morbid lyrics. .. a person who wears mostly black clothing, used dark dramatic makeup, and often has dyed black hair.”
Here is a description from the “Gothic and Lolita History” by Michelle Nguyen; ” Gothic Lolitas – The dark Lolitas who wear dark colors and typically have straight raven (black) hair and long false eyelashes, along with dramatic makeup to present a slightly evil-yet-innocent appearance.” (Gothic Lolitas being one of four sub types of “Classic Gothic Lolita.”) (The others being “Sweet Lolitas,” “Punk Lolitas,” and “Aristocrat Lolitas.”)